1. Field of the Invention
The present invention relates to an exhaust system for an engine.
2. Description of the Related Art
In a conventional engine, for example, to maintain the exhaust gas, flowing into the catalyst arranged in the exhaust passage, at a high temperature, a double exhaust pipe, comprising an outer pipe and an inner pipe arranged to lie spaced from the inner circumferential wall of the outer pipe, is used. In such a double exhaust pipe, normally, one of the ends of the inner pipe is fixed to the inner circumferential wall of the outer pipe by welding, and the other end of the inner pipe is supported by the outer pipe via a heat insulating retainer formed of wire mesh so that the other end of the inner pipe is able to move in the axial direction relative to the outer pipe. However, the wire mesh prevents, to some extent, the exhaust gas from passing through (For an example, see FIG. 1 of the Japanese Utility Model publication No. 63-130616).
However, such a double exhaust pipe normally has a construction such that the exhaust gas flows directly over the portion of the inner wall welded to the outer pipe, and thus, the temperature of the area of the outer pipe near the welded portion of the inner pipe becomes excessively high. Nevertheless, if an area in which the temperature becomes extremely high exists on the exhaust pipe, the outer pipe must be formed of a material which is able to tolerate an extremely high temperature, and thus, a problem occurs in that the manufacturing cost of the double exhaust pipe increases considerably.